fix(shared-help): harden help system with XSS protection, i18n, type safety, and reference implementation

- Add HTML sanitization via isomorphic-dompurify in parser layer to prevent XSS
- Replace all hardcoded English strings with translations (FAQSection, KeyboardShortcuts, ChangelogEntry/Section)
- Remove unsafe `as` type casting in loader.ts, use Zod-inferred generics instead
- Add error logging in content loader (replaces silent catch blocks)
- Fix HelpSearch blur handling (mousedown+preventDefault instead of setTimeout hack)
- Add ARIA attributes to HelpSearch for accessibility
- Derive FAQ categories from items instead of hardcoding all 6
- Fix null-safety in GettingStartedGuide.svelte
- Fix unused appId variable in HelpPage.svelte, add scroll-reset on tab switch
- Rebuild Contacts help page as reference implementation using shared HelpPage component
- Add README with quick-start guide, props docs, and translations template

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/shared-help-content/package.json

@@ -34,9 +34,11 @@
 		"@manacore/shared-help-types": "workspace:*",
 		"fuse.js": "^7.0.0",
 		"gray-matter": "^4.0.3",
+		"isomorphic-dompurify": "^3.7.1",
 		"marked": "^15.0.4"
 	},
 	"devDependencies": {
+		"@types/dompurify": "^3.2.0",
 		"@types/node": "^22.10.2",
 		"typescript": "^5.7.3",
 		"zod": "^3.24.1"